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Message-ID: <CAGXu5jJTEoeGs8uBdHYdBJwacOp2b22ySrn-V8T93qaD4cv65A@mail.gmail.com>
Date: Tue, 27 Jun 2017 16:05:55 -0700
From: Kees Cook <keescook@...omium.org>
To: Salvatore Mesoraca <s.mesoraca16@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Brad Spengler <spender@...ecurity.net>, PaX Team <pageexec@...email.hu>,
Casey Schaufler <casey@...aufler-ca.com>, James Morris <james.l.morris@...cle.com>,
"Serge E. Hallyn" <serge@...lyn.com>, Linux-MM <linux-mm@...ck.org>, "x86@...nel.org" <x86@...nel.org>,
Jann Horn <jannh@...gle.com>, Christoph Hellwig <hch@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>, Stephen Smalley <sds@...ho.nsa.gov>,
John Johansen <john.johansen@...onical.com>
Subject: Re: [RFC v2 3/9] Creation of "check_vmflags" LSM hook
On Thu, Jun 15, 2017 at 9:42 AM, Salvatore Mesoraca
<s.mesoraca16@...il.com> wrote:
> Creation of a new LSM hook to check if a given configuration of vmflags,
> for a new memory allocation request, should be allowed or not.
> It's placed in "do_mmap", "do_brk_flags" and "__install_special_mapping".
I like this. I think this is something the other LSMs should be
checking too. (Though I wonder if it would be helpful to include the
VMA in the hook, though it does exist yet, so... hmm.)
-Kees
>
> Signed-off-by: Salvatore Mesoraca <s.mesoraca16@...il.com>
> ---
> include/linux/lsm_hooks.h | 7 +++++++
> include/linux/security.h | 6 ++++++
> mm/mmap.c | 13 +++++++++++++
> security/security.c | 5 +++++
> 4 files changed, 31 insertions(+)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index bd274db..33dab16 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -483,6 +483,11 @@
> * @reqprot contains the protection requested by the application.
> * @prot contains the protection that will be applied by the kernel.
> * Return 0 if permission is granted.
> + * @check_vmflags:
> + * Check if the requested @vmflags are allowed.
> + * @vmflags contains requested the vmflags.
> + * Return 0 if the operation is allowed to continue otherwise return
> + * the appropriate error code.
> * @file_lock:
> * Check permission before performing file locking operations.
> * Note: this hook mediates both flock and fcntl style locks.
> @@ -1477,6 +1482,7 @@
> unsigned long prot, unsigned long flags);
> int (*file_mprotect)(struct vm_area_struct *vma, unsigned long reqprot,
> unsigned long prot);
> + int (*check_vmflags)(vm_flags_t vmflags);
> int (*file_lock)(struct file *file, unsigned int cmd);
> int (*file_fcntl)(struct file *file, unsigned int cmd,
> unsigned long arg);
> @@ -1747,6 +1753,7 @@ struct security_hook_heads {
> struct list_head mmap_addr;
> struct list_head mmap_file;
> struct list_head file_mprotect;
> + struct list_head check_vmflags;
> struct list_head file_lock;
> struct list_head file_fcntl;
> struct list_head file_set_fowner;
> diff --git a/include/linux/security.h b/include/linux/security.h
> index af675b5..8701872 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -300,6 +300,7 @@ int security_mmap_file(struct file *file, unsigned long prot,
> int security_mmap_addr(unsigned long addr);
> int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> unsigned long prot);
> +int security_check_vmflags(vm_flags_t vmflags);
> int security_file_lock(struct file *file, unsigned int cmd);
> int security_file_fcntl(struct file *file, unsigned int cmd, unsigned long arg);
> void security_file_set_fowner(struct file *file);
> @@ -823,6 +824,11 @@ static inline int security_file_mprotect(struct vm_area_struct *vma,
> return 0;
> }
>
> +static inline int security_check_vmflags(vm_flags_t vmflags)
> +{
> + return 0;
> +}
> +
> static inline int security_file_lock(struct file *file, unsigned int cmd)
> {
> return 0;
> diff --git a/mm/mmap.c b/mm/mmap.c
> index f82741e..132061b 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1311,6 +1311,7 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
> {
> struct mm_struct *mm = current->mm;
> int pkey = 0;
> + int error;
>
> *populate = 0;
>
> @@ -1363,6 +1364,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
> vm_flags |= calc_vm_prot_bits(prot, pkey) | calc_vm_flag_bits(flags) |
> mm->def_flags | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
>
> + error = security_check_vmflags(vm_flags);
> + if (error)
> + return error;
> +
> if (flags & MAP_LOCKED)
> if (!can_do_mlock())
> return -EPERM;
> @@ -2833,6 +2838,10 @@ static int do_brk_flags(unsigned long addr, unsigned long request, unsigned long
> return -EINVAL;
> flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
>
> + error = security_check_vmflags(flags);
> + if (error)
> + return error;
> +
> error = get_unmapped_area(NULL, addr, len, 0, MAP_FIXED);
> if (offset_in_page(error))
> return error;
> @@ -3208,6 +3217,10 @@ static struct vm_area_struct *__install_special_mapping(
> int ret;
> struct vm_area_struct *vma;
>
> + ret = security_check_vmflags(vm_flags);
> + if (ret)
> + return ERR_PTR(ret);
> +
> vma = kmem_cache_zalloc(vm_area_cachep, GFP_KERNEL);
> if (unlikely(vma == NULL))
> return ERR_PTR(-ENOMEM);
> diff --git a/security/security.c b/security/security.c
> index 42c8028..7e45846 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -900,6 +900,11 @@ int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot,
> return call_int_hook(file_mprotect, 0, vma, reqprot, prot);
> }
>
> +int security_check_vmflags(vm_flags_t vmflags)
> +{
> + return call_int_hook(check_vmflags, 0, vmflags);
> +}
> +
> int security_file_lock(struct file *file, unsigned int cmd)
> {
> return call_int_hook(file_lock, 0, file, cmd);
> --
> 1.9.1
>
--
Kees Cook
Pixel Security
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